This invention relates to tree felling apparatus such as a chain saw and more particularly to such apparatus mountable to a vehicle for mechanically harvesting trees
Over the years a number of types of felling apparatus mountable to a tractor or similar vehicle have been developed for mechanically harvesting trees. One type of apparatus employs hydraulically powered shears for slicing through the tree. Another type of apparatus employs a chain saw that pivotally swings across a defined opening in which a tree is situated.
The primary drawback of shear type apparatus is the damage to the wood fiber caused by the compression required to force the blades laterally through the tree trunk. The tree may also split as the blade nears the end of its normal stroke. Trees with such splits provide a lower overall yield of lumber or pulp chips.
Chain saw type felling apparatus avoids the damage to the trees caused by shears, but such apparatus provided heretofore suffer from other drawbacks. U.S Pat. No. 4,462,439, for example, discloses a chain saw comprising a cutting chain supported on a plate or bar and mounted on the front of a tractor for felling trees. The bar is pivotally attached to a supporting frame which is notched to receive a tree. In cutting a tree positioned within the notch, the saw is hydraulically pivoted through an arc from one edge of the notch into a recess in the opposite side. As the saw nears the end of the cut, the weight of the tree is shifted entirely onto the saw. With repeated usage, this weight can bend the saw bar or damage the chain. Moreover, the saw is pivoted by a linear actuator, which causes the rate of feed of the saw through the tree trunk to vary and produce a nonuniform cut.
U.S. Pat. No. 3,604,479 discloses a similar apparatus in which a chain saw supported on a bar is mounted to the front of a vehicle The saw bar is pivoted across an opening in which the tree is received toward the blunt side of a stationary jaw. As the saw nears the end of its cut, the tree's weight is borne by the saw bar. The saw chain is also unprotected and can be easily damaged from the pivoting action of the falling tree.
Other chain saw type apparatus are disclosed in U.S. Pat. Nos. 3,364,960 and 4,273,169. Both utilize pivotal chain saws that suffer from the drawbacks discussed herein.